1. Field of the Invention
The present invention relates to a scroll hydraulic machine used as a compressor or an expansion device. The present application is based on Japanese Patent Application No. 9-24466, the contents of which are herein incorporated by reference.
2. Description of Related Art
To a hydraulic machine having a fixed scroll and a swirling scroll engaging with the fixed scroll and performing a swirling motion, there is provided an Oldham joint making the swirling scroll perform a revolutionary swirling motion while preventing the swirling scroll from rotating. The fixed scroll, the swirling scroll and the Oldham joint, together with the other parts, are disposed within a housing formed by a case body and a front case attached to an opening of an end thereof.
A vertical cross section of the conventional front case is shown in FIG. 3, in which an Oldham joint and a front case 6 are connected to each other by a key formed in the Oldham joint and a key groove 50 penetrating the front case 6. Further, a thrust bearing 36 supporting a thrust force acting on the swirling scroll is disposed at a peripheral edge of the inner end surface of the front case 6.
In the conventional scroll hydraulic machine described above, for the purpose of reducing weight and making it light, the case body, the front case, the fixed scroll, and the swirling scroll have been normally made of an aluminum alloy.
However, since the Oldham joint is formed of a ferrous alloy and the surface thereof is hardened by a heat treatment, there has been a problem in that, when lubricating oil runs out, the key groove 50 in the front case 6 is abnormally abraded. Further, since it is necessary to provide the thrust bearing, there has been a problem in that the number of the parts is increased, the increasing cost.